Internal gear pump

ABSTRACT

An internal gear pump for delivering a fluid, in particular one of the gerotor pump type, having a driven gear wheel, a rotatable annular gear interacting with the gear wheel, and a substantially cylindrical housing, in which the gear wheel and the annular gear are arranged. The housing has a base portion, an annular portion and a cover portion, the base portion having a pressure port, which forms a delivery chamber of the pump or opens into the latter. A thrust ring is arranged between the gear wheel and the annular gear on the one hand and the cover portion of the housing on the other. At least one connecting passage on or in the housing of the pump extends from the delivery chamber of the pump up to a gap between the thrust ring and the cover portion of the housing, in order to carry fluid from the delivery chamber into the gap.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to GermanPatent Application No. 10 2011 017 374 (filed on Apr. 1, 2011), which ishereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to an internal gear pump for delivering a fluid,in particular one of the gerotor pump type.

BACKGROUND OF THE INVENTION

Such an internal gear pump has a driven gear wheel (also referred to asan inner rotor) and an annular gear (also referred to as an externalrotor) interacting with the gear wheel, the annular gear having at leastone tooth more than the gear wheel.

FIG. 7 illustrates a cross-sectional view of a conventional gerotor pump101 (also referred to as an annular gear pump). The pump 101 has asubstantially cylindrical housing having an annular portion 103. Anannular gear 105 is supported on the circular inner circumference of theannular portion 103 so that it is free to rotate about an axis A1. Agear wheel 107, which is driven by way of a drive shaft (not shown) torotate clockwise about an axis A2, for example, is arranged radiallyinside the annular gear 105 and eccentrically in relation to the annulargear 105. The gear wheel 107 has an external toothing, and the annulargear 105 has an internal toothing with a greater number of teeth thanthat of the gear wheel 107. The gear wheel 107 meshes with the annulargear 105 and thereby drives the annular gear 105 to rotate. Owing to thegreater number of teeth, however, the annular gear 105 rotates moreslowly than the gear wheel 107.

Also illustrates in FIG. 7 are a suction port 109 and a pressure port111, which are formed on a base portion 113 of the pump housing, onwhich the annular gear 105 and the gear wheel 107 rest. Axially offsetfrom the base portion 113 relative to the axes A1, A2, the annular gear105 and the gear wheel 107 are covered by a cover portion of the housing(not shown). Due to the rotation of the gear wheel 107 relative to thehousing (annular portion 103, base portion 113 and cover portion),rotating pump chambers of variable volume, into which a fluid is drawnfrom the suction port 109, are formed between the gear wheel 107 and theannular gear 105. The fluid is finally expelled into a pressure chamber115 of the pump 101, into which the pressure port 111 opens or which isformed by the pressure port 111 itself.

One particular problem of such an internal gear pump is the frictionbetween the gear wheel 107 and the annular gear 105 on the one hand andthe surrounding portions of the housing on the other. This frictioncauses an unwanted loss of power, which is accompanied by a heating andimpairment of the fluid.

German Patent Publication DE 43 15 432 A1, therefore, discloses thearrangement of a thrust ring, which is rotationally fixed to therotating annular gear, between the gear wheel and the annular gear onthe one hand and the cover portion of the housing on the other. Thethrust ring reduces the power loss by virtue of a reduction in thedifferential speed and hence a reduction in the friction. In particular,the thrust ring may be composed of a material having a low coefficientof friction, or it may be provided with a coating of a material having alow coefficient of friction. This is comparatively costly, however, andeven then still does not bring about the feasible reduction of thefriction losses consistent with cost-effective manufacturing.

SUMMARY OF THE INVENTION

An object of the invention is to create an internal gear pump of saidtype, which being of simple construction exhibits a low degree offriction between the gear wheel and the annular gear on the one hand andthe housing on the other.

A further object of the invention is to stabilize the alignment of thegear wheel.

At least these objects are achieved by an internal gear pump thatincludes at least the following: a thrust ring arranged between a gearwheel and an annular gear on the one hand and a cover portion of thehousing on the other, at least one connecting passage on or in thehousing of the pump extending from the delivery chamber of the pump upto a gap between the thrust ring and the cover portion of the housing,in order to carry fluid from the delivery chamber into the gap.

At least these objects are further achieved by an internal gear pumpthat includes at least the following: a driven gear wheel; a rotatableannular gear operatively communicating with the driven gear wheel; ahousing in which the driven gear wheel and the rotatable annular gearare arranged, the housing comprising a base portion, an annular portionand a cover portion, the base portion having a pressure port which formsa fluid delivery chamber; a thrust ring arranged between the driven gearwheel and the rotatable annular gear and also the driven gear wheel andthe cover portion; a gap formed between the thrust ring and the coverportion; and at least one fluid connecting passage extending from thefluid delivery chamber up to the gap in order to carry fluid from thedelivery chamber into the gap.

At least these objects are also achieved by an internal gear pump thatincludes at least the following: a gear wheel which is rotatable about afirst axis; an annular gear which is rotatable about a second axis; athrust ring rotationally fixed to the annular gear; a housing whichhouses the gear wheel, the annular gear and the thrust ring, the housinghaving a fluid delivery chamber and a cover portion; a gap formedbetween the thrust ring and the cover portion; and a fluid connectingpassage in the housing through which fluid flows from the fluid deliverychamber to the gap to thereby form a hydrodynamic lubricating film inthe gap which reduces operational friction between the thrust ring andthe cover portion.

At least these objects are further achieved by an internal gear pumpthat includes at least the following: a gear wheel; an annular gear; athrust ring; a housing having a fluid delivery chamber and a coverportion configured for placement such that a gap is formed between thethrust ring and the cover portion; and a fluid connecting passagethrough a fluid flows from the fluid delivery chamber to the gap tothereby form a hydrodynamic lubricating film in the gap which reducesoperational friction between the thrust ring and the cover portion. Thefluid connecting passage has a first connecting groove in communicationwith the fluid delivery chamber, a second connecting groove incommunication with the first connecting groove, and a third connectinggroove in communication with the second connecting groove and the gap.The thrust ring has a plurality of distribution grooves on a surfacethereof which faces the gap and which are configured to distribute thefluid into the gap.

Between the thrust ring and the inside of the cover portion of thehousing facing the thrust ring a gap is formed, which may extend overthe entire surface of the thrust ring or merely a part thereof. Aconnecting passage on or in the housing of the pump leads from thedelivery chamber of the pump up to the gap, in particular right behindthe thrust ring, when viewed from the base portion of the housing. Thepressurized fluid can therefore flow from the delivery chamber up to thegap, in order to build up a hydraulic pressure between the thrust ringand the cover portion of the housing and to form a hydrodynamicallyeffective lubricating film as the thrust ring rotates.

It is possible here that the gap will only actually be formed by thepressurized fluid flowing in between the thrust ring and the coverportion of the housing. In other words, although the thrust ring mayrest directly on the cover portion of the housing when the pump is at astandstill, when the pump is in operation it is important that a minimumclearance be provided between the thrust ring and the cover portion ofthe housing, in order to allow the formation of a fluid cushion or alubricating film. For this purpose the fluid delivered by the pump isspecifically carried along the connecting passage up to the gap betweenthe rotor disc and the cover portion of the housing, the pressurizedfluid, when necessary, being structurally configured to lift the thrustring off slightly from the cover portion of the housing.

This results in a hydrodynamic lubrication, which serves to reduce thepower loss still further. The additional design cost is minimal, sincethe connecting passage can be formed on or in the pump housing throughsimple production operations. A further advantage consists in thatfeeding the pressurized fluid to the rear side of the thrust ring exertsa force, which serves to reduce or even avoid any tilting or wobbling ofthe gear wheel. Furthermore, the specifically diverted fluid serves forhydraulically centring the annular gear, thereby increasing the servicelife of the pump still further.

The thrust ring is preferably rotationally fixed to the annular gear. Inparticular, the annular gear and the thrust ring may be integrallyformed. Alternatively, however, the thrust ring may also be rotatablycoupled to the gear wheel, or the thrust ring is “floating,” that is tosay, supported so that it is free to rotate.

Where, in connection with the pump in accordance with the invention,reference is made to a “base portion” of the housing, this relates tothe portion of the housing on which the pressure port is provided, whichopens into the delivery chamber of the pump or which forms the deliverychamber. Where reference is made to a “cover portion” of the housing,this relates to the portion of the housing on which the thrust ringrests. In other words, the terms “base portion” and “cover portion” ofthe housing are used irrespective of whether the “base portion” in thepump installation position is arranged on an underside or an upper sideof the pump, for example.

The connecting passage may be formed by one or more bores in the housingof the pump, for example, in particular by a bore in the base portion ofthe housing and/or by a bore in the annular portion of the housing.

In accordance with a preferred embodiment, however, the connectingpassage includes at least one connecting groove, which extends along theinner circumference of the annular portion of the housing. It istherefore only necessary to apply a groove to the inside of the pumphousing, for example by machining or by moulding, in order to carry thepressurized fluid up to the gap. The connecting groove in the annularportion of the housing may extend, for example, up to the transitionbetween the annular portion and the cover portion of the housing. Theconnecting groove along the inner circumference of the annular portionof the housing preferably extends parallel to the axis of rotation ofthe annular gear. Alternatively, the connecting groove may also beslanted at an angle conducive to the flow and need not necessarily havea rectilinear course.

Such an “axial” connecting groove may emerge directly from the deliverychamber of the pump. Alternatively, a further connecting groove may beprovided, which extends from the delivery chamber of the pump along theinside of the base portion of the housing up to the connecting groove inthe annular portion of the housing, in particular radially outwards, inorder to form a duct of L-shaped longitudinal section for the fluid.

In accordance with an advantageous embodiment the connecting passage (inparticular the connecting groove in the annular portion of the housing)opens into an annular groove, which extends circumferentially along thetransition between the annular portion and the cover portion of thehousing and/or along the thrust ring. This allows the pressurized fluidto be distributed along the circumference of the thrust ring and/or thecover portion of the housing, in order to penetrate into the gap betweenthe thrust ring and the cover portion of the housing in multipledifferent angular positions, and therefore, to form a lubricating filmthat is as uniform as possible.

It is particularly advantageous if the cover portion of the housingincludes at least one distribution groove, which extends radiallyinwards on the inside of the cover portion facing the thrust ring. Thisis particularly effective in conducting the fluid into the gap betweenthe thrust ring and the cover portion of the housing, in order to formthe desired lubricating film. To do this the respective distributiongroove need not extend radially inwards in an exact straight line, othercourses and alignments also being possible (for example, a slantingalignment, a laterally offset arrangement or a curved path with acomponent directed radially inwards). The distribution groove preferablyextends radially inwards starting from the transition between theannular portion and the cover portion of the housing and/or from theannular groove. A plurality of such distribution grooves are preferablyprovided.

With regard to the distribution groove in the cover portion of thehousing it is preferred, in order to avoid additional leakage losses, ifthis groove has only a limited length, that is to say if thedistribution groove does not extend radially inwards all the waythrough. In other words, the distribution groove is in this case to beformed as a stepped groove. This is particularly important if the thrustring and/or the cover portion of the housing has a central through-holefor a drive shaft. If additional leakage is required, however, it isalternatively advantageous if the distribution groove of the coverportion is continuous, that is to say if the distribution groove extendsradially all the way inwards.

Alternatively, or in addition to the distribution groove in the coverportion of the housing, on the side facing the cover portion (that is tosay on its rear side) the thrust ring may also have at least onedistribution groove, which extends radially inwards from the outercircumference of the thrust ring. Such a distribution groove on thethrust ring also serves to enhance the distribution of the pressurizedfluid inside the gap between the thrust ring and the cover portion ofthe housing, so that a more uniform build-up of pressure and a moreefficient hydrodynamic lubrication is obtained. The distribution groovein the thrust ring also need not be aligned radially inwards in an exactstraight line, other courses and alignments being feasible.

With regard to the distribution groove in the thrust ring it is likewisepossible for this to have a limited length, in order to reduce leakagelosses in the radially inner area of the pump. Alternatively, thedistribution groove in the thrust ring may extend radially inwards allthe way through, in order to bring about a specific leakage, asexplained above in connection with the distribution groove in the coverportion of the housing.

In an accordance with another embodiment of an advantageously simpledesign, the side of the thrust ring facing the cover portion of thehousing may be of plane design. It is also advantageous, however, if theside of the thrust ring facing the cover portion of the housing is oftapered design, truncated cone-shaped design or convexly curved. Such ashaping of the thrust ring is a simple way of ensuring that along theentire circumference a minimum gap always exists between the thrust ringand the cover portion of the housing, at least in a radially outer area,in order to ensure an efficient hydrodynamic lubrication.

Alternatively, or in addition to this, the inside of the cover portionof the housing facing the thrust ring may also be of tapered design,truncated cone-shaped design or convexly curved. In these embodimentsdistribution grooves may additionally be provided on the cover portionof the housing and/or on the thrust ring, in particular without or withspecific leakage, as explained above.

Where a specific leakage of the fluid carried into the gap between thethrust ring and the cover portion of the housing is brought about (forexample, by a distribution groove in the cover portion or the thrustring extending radially inwards all the way through), an advantage maylie, for example, in a reduced pressure level at higher rotationalspeeds (lower mechanical losses). Furthermore, such a specific leakagecreates an additional facility for cooling the pump and/or the fluid.Such a specific leakage can furthermore serve to provide an interimstorage of fluid not needed in certain operating states.

As an alternative or addition, in the case of such a specific leakagethe fluid (particularly if the fluid is a lubricating oil) may be usedfor the lubrication of components close to the pump (for example throughthe use of a slinger ring). For example, the fluid may be carried out ofthe gap or directly out of the distribution groove to another component,which is arranged on or adjacent to the pump. In particular, the housingof the pump may have an outlet port, in order to conduct a proportion ofthe fluid, carried out of the delivery chamber towards the gap, toanother component and thereby to lubricate the latter. The outlet portmay, in particular, be provided in a radially inner area of the pumphousing, for example, in the area of a central through-hole in the coverportion of the housing intended for a drive shaft. However, such athrough-hole in the cover portion intended for a drive shaft need not bepresent in all embodiments of a pump in accordance with the invention.

It is furthermore preferred if the thrust ring extends in one piece in aradial direction between the gear wheel and the annular gear. In otherwords, the thrust ring in accordance with this embodiment should atleast partially cover not only the annular gear, but also the gear wheelin a radial direction, there being no possibility for directcommunication of the gap (hydrodynamic lubrication gap between thethrust ring and the cover portion of the housing) with the pumpchambers, which are formed between the gear wheel and the annular gear.For a simple construction, the thrust ring therefore ensures that nosignificant leakage losses occur in an axial direction (relative to theaxis of rotation of the gear wheel and of the annular gear).

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous refinements of the invention will emerge from the dependentclaims. An exemplary embodiment of the invention will be discussed inprinciple below on the basis of the drawing, in which:

FIG. 1 illustrates a view in longitudinal section through an internalgear pump.

FIG. 2 illustrates a cross-sectional view of an internal gear pump.

FIGS. 3 a and 3 b illustrates a top view and a side view respectively ofa thrust ring in accordance with embodiments.

FIG. 4 illustrates a top view of a thrust ring in accordance withembodiments.

FIG. 5 illustrates a view in longitudinal section through a thrust ringin accordance with embodiments.

FIG. 6 illustrates a view in longitudinal section through a thrust ringin accordance with embodiments.

FIG. 7 illustrates a cross-sectional view of a conventional internalgear pump.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates an internal gear pump 1 in accordance with theinvention of the gerotor pump type. The pump 1 includes a gear wheel 7,which is driven to rotate about an axis A2 by a shaft 17 passing throughthe pump. The pump 1 further includes a freely rotatable annular gear 5,that is to say an internal gear, the internal toothing of which mesheswith the external toothing of the gear wheel 7. The axis of rotation A1of the annular gear 5 is eccentric to the axis of rotation A2 of thegear wheel 7. A thrust ring 19 is rotationally fixed to the annular gear5, for example, via weld or bond. Alternatively, the thrust ring 19 isintegrally formed with the annular gear 5. The thrust ring 19 may becomposed, for example, of steel. Apart from a central through-hole forthe shaft 17, the thrust ring 19 is closed (that is to say it is withoutapertures) and is formed in one piece. The outside diameter of thethrust ring 19 corresponds to or is otherwise substantially equal tothat of the annular gear 5.

The gear wheel 7, the annular gear 5 and the thrust ring 19 areaccommodated in a housing of the pump 1, which includes a hollowcylindrical annular portion 3. The annular gear 5 is rotatably supportedon the inner circumference of the annular portion 3.

The housing of the pump 1 further includes a base portion 13, on whichthe gear wheel 7 and the annular gear 5 rest and which in the exemplaryembodiment illustrated in FIG. 1 is integrally formed with the annularportion 3. A delivery chamber 15 of the pump 1 is formed in the baseportion 13 of the housing The housing of the pump 1 further includes acover portion 21, which in the exemplary embodiment illustrated in FIG.1 takes the form of a separate cover.

The thrust ring 19 is arranged spatially between the gear wheel 7 andthe annular gear 5 on the one hand and the cover portion 21 of thehousing on the other. A gap 23 of very narrow size is formed between thethrust ring 19 and the cover portion 21. Inside the housing the gearwheel 7, the annular gear 5 and/or the thrust ring 19 may bepre-tensioned in an axial direction relative to the axes of rotation A1,A2 (not illustrated).

When the pump 1 is in operation, the annular gear 5, together with thethrust ring 19 coupled thereto, rotates more slowly than the gear wheel7. The thrust ring 19 therefore contributes to a certain reduction ofthe friction losses, since the differential speed between the gear wheel7 and the cover portion 21 is effectively reduced owing to thearrangement of the thrust ring 19 between the gear wheel 7 and the coverportion 21 of the housing.

A further reduction of the friction losses is achieved in the internalgear pump 1 in accordance with the embodiment illustrated in FIG. 1 inthat a connecting passage on the housing of the pump 1 extends from thedelivery chamber 15 up to the gap 23 between the thrust ring 19 and thecover portion 21 of the housing. Pressurized fluid is carried from thedelivery chamber 15 along the connecting passage into the gap 23, thefluid in the gap 23 forming a hydrodynamically effective lubricatingfilm.

For this purpose the connecting passage comprises a connecting groove25, which on the inside of the base portion 13 of the housing facing theannular gear 5 extends in a radial direction from the delivery chamber15 up to the inner circumference of the annular portion 3 of thehousing. The radial connecting groove 25 is circumferentially closed bythe underside of the annular gear 5. The radial connecting groove 25opens into and is in communication with an axial connecting groove 27 ofthe connecting passage, and extends along the inner circumference of theannular portion 3 of the housing parallel to the axis of rotation A1 ofthe annular gear 5. The axial connecting groove 27 is circumferentiallyclosed by the outer circumference of the annular gear 5. The radialconnecting groove 25 and the axial connecting groove 27, therefore, forma duct of L-shaped longitudinal cross-section as illustrated in FIG. 1for the fluid of the pump 1. The connecting grooves 25, 27 may form across-sectional aperture of between 1 to 5 mm², for example, aperturesof a different cross section naturally also being possible. The suitablecross section generally depends on the output of the pump, the viscosityof the fluid and the pressure range of the pump.

The axial connecting groove 27 opens at the transition between theannular portion 3 and the cover portion 21 of the housing into a radialdistribution groove 29. The radial distribution groove 29 is formed onthe inside, that is to say, on the side of the cover portion 21 of thehousing facing the thrust ring 19, and which, extending radially inward,is of limited length. Through the connecting passage comprisingconnecting grooves 25, 27 and distribution groove 29, a proportion ofthe fluid delivered by the pump 1 can pass or otherwise flow from thedelivery chamber 15 into the gap 23 between the thrust ring 19 and thecover portion 21 of the housing, in order to form a hydrodynamicallyeffective lubricating film in the gap 23. The lubricating film actsbetween the rotating thrust ring 19 and the fixed cover portion 21 ofthe housing. The friction between the thrust ring 19 and the coverportion 21 of the housing is thereby considerably reduced. Thiscontributes to a reduced wear and reduced heating and impairment of thefluid.

The cover portion 21 of the housing may obviously comprise a pluralitydistribution grooves 29, particularly in a regular angular arrangement,in order to achieve a more uniform distribution of the fluid along thecircumference of the thrust ring 19. For this purpose a separateconnecting passage, emerging from the delivery chamber 15, may beprovided for each distribution groove 29 in the cover portion 21.Alternatively, an annular groove (not illustrated), which distributesthe fluid delivered from the delivery chamber 15 along the connectinggrooves 25, 27 along the circumference of the thrust ring 19 or thecover portion 21 of the housing, may be provided on the annular portion3 of the housing, on the cover portion 21 of the housing and/or alongthe outer circumference of the thrust ring 19.

FIG. 2 illustrates a cross-sectional view of an internal gear pump inaccordance with the invention. FIG. 2 illustrates the radial connectinggroove 25 in the base portion 13 and the axial connecting groove 27 inthe annular portion 3 of the housing, which form the connecting passagedescribed, extending from the delivery chamber 15 to the thrust ring 19and the cover portion 21 of the housing.

As illustrated in FIGS. 3 a and 3 b, alternatively or in addition to theformation of a distribution groove 29 along the cover portion 21 of thehousing illustrated in FIG. 1, one or more distribution grooves 31 maybe provided on a surface of the rear side 33 of the thrust ring 19facing the gap 23 (that is to say, on the upper side of the thrust ring19 in the representation illustrated in FIG. 1). As illustrated in FIGS.3 a and 3 b, a plurality if of radial distribution grooves 31 areprovided, asymmetrically formed and arranged with a slight lateraloffset.

In the embodiment illustrated in FIGS. 3 a and 3 b the distributiongrooves 31 in the thrust ring 19 are formed all the way through, that isto say they extend from the outer circumference up to the innercircumference (central through-hole for the shaft 17). In this wayspecifically desired leakage effects can be produced, for example, for abuild-up of pressure, additional cooling or the lubrication of furthercomponents by leakage oil.

As illustrated in FIG. 4, alternatively, the distribution grooves 31 areformed as stepped grooves, which extend radially inwards only along alimited length from the outer circumference of the thrust ring 19, forexample, up to approximately 1 mm from the inner circumference of thethrust ring 19. This serves to minimize leakage losses.

In the embodiments illustrated in FIGS. 1, 3 a, 3 b and 4, the rear side33 of the respective thrust ring 19 is of plane design.

As illustrated in FIG. 5, alternatively, the rear side 33 of the thrustring 19 facing the cover portion 21 of the housing may be of tapereddesign. This serves, as an alternative or addition to the provision ofdistribution grooves 31, to bring about an enhanced distribution of thefluid delivered via the connecting passage.

As illustrated in FIG. 6, alternatively, the rear side 33 of the thrustring 19 may have a bowed or arcuate design, that is to say, of convexlycurved design. This serves, as an alternative or addition to theprovision of distribution grooves 31, to bring about an enhanceddistribution of the fluid delivered via the connecting passage.

Alternatively or in addition to such a tapered, truncated cone-shaped orconvexly curved design of the rear side 33 of the thrust ring 19, theinside surface of the cover portion 21 of the housing (FIG. 1) facingthe thrust ring 19 may be of tapered, truncated cone-shaped or convexlycurved design. In both cases, the gap 23 between the thrust ring 19 andthe cover portion 21 of the housing (FIG. 1) has, at least in portions,an overall height diminishing radially inwards.

Although embodiments have been described herein, it should be understoodthat numerous other modifications and embodiments can be devised bythose skilled in the art that will fall within the spirit and scope ofthe principles of this disclosure. More particularly, various variationsand modifications are possible in the component parts and/orarrangements of the subject combination arrangement within the scope ofthe disclosure, the drawings and the appended claims. In addition tovariations and modifications in the component parts and/or arrangements,alternative uses will also be apparent to those skilled in the art.

1. A gear pump for delivering a fluid, comprising: a driven gear wheel;a rotatable annular gear operatively communicating with the driven gearwheel; a housing in which the driven gear wheel and the rotatableannular gear are arranged, the housing comprising a base portion, anannular portion and a cover portion, the base portion having a pressureport which forms a fluid delivery chamber; a thrust ring arrangedbetween the driven gear wheel and the rotatable annular gear and alsothe driven gear wheel and the cover portion; a gap formed between thethrust ring and the cover portion; and at least one fluid connectingpassage extending from the fluid delivery chamber up to the gap in orderto carry fluid from the delivery chamber into the gap.
 2. The gear pumpof claim 1, wherein the connecting passage comprises at least oneconnecting groove which extends along the inner circumference of theannular portion of the housing.
 3. The gear pump of claim 2, wherein theconnecting groove along the inner circumference of the annular portionis aligned parallel to the axis of rotation of the rotatable annulargear.
 4. The gear pump of claim 1, wherein the connecting passagecomprises a connecting groove which extends from the delivery chamber ofthe pump along the base portion of the housing.
 5. The gear pump ofclaim 1, wherein the connecting passage opens into an annular groovewhich extends circumferentially along a transition between the annularportion and the cover portion of the housing and along the thrust ring.6. The gear pump of claim 1, wherein the cover portion of the housingcomprises at least one distribution groove which extends radially inwardon the inside surface of the cover portion.
 7. The gear pump of claim 6,wherein the distribution groove of the cover portion extends radiallyinward from the outer circumference of the cover portion to a centralaperture of the cover portion.
 8. The gear pump of claim 1, wherein thethrust ring comprises at least one distribution groove which on the sideof the thrust ring facing the cover portion of the housing extendsradially inward from the outer circumference of the thrust ring.
 9. Thegear pump of claim 8, wherein the distribution groove of the thrust ringextends radially inward from the outer circumference of the thrust ringto a central aperture of the thrust ring.
 10. The gear pump of claim 1,wherein the surface of the thrust ring facing the cover portion of thehousing is one of tapered, truncated cone shape, and convexly curved.11. The gear pump of claim 1, wherein the housing comprises an outletport configured to conduct a proportion of the fluid, carried out of thedelivery chamber towards the gap, to another component to therebylubricate the component.
 12. The gear pump of claim 1, wherein thethrust ring extends in one piece in a radial direction between thedriven gear wheel and the rotatable annular gear.
 13. The gear pump ofclaim 1, wherein the thrust ring is rotationally fixed to the annulargear.
 14. The gear pump of claim 1, wherein the rotatable annular gearand the thrust ring are integrally formed.
 15. A gear pump for a gerotorpump, the gear pump comprising: a gear wheel which is rotatable about afirst axis; an annular gear which is rotatable about a second axis; athrust ring rotationally fixed to the annular gear; a housing whichhouses the gear wheel, the annular gear and the thrust ring, the housinghaving a fluid delivery chamber and a cover portion; a gap formedbetween the thrust ring and the cover portion; and a fluid connectingpassage in the housing through which fluid flows from the fluid deliverychamber to the gap to thereby form a hydrodynamic lubricating film inthe gap which reduces operational friction between the thrust ring andthe cover portion.
 16. The gear pump of claim 15, wherein the fluidconnecting passage comprises: a first connecting groove extendingradially and in communication with the fluid delivery chamber; a secondconnecting groove extending axially and in communication with the firstconnecting groove; and a third connecting groove extending radially andin communication with the second connecting groove and the gap.
 17. Thegear pump of claim 15, wherein the thrust ring has a plurality ofdistribution grooves on a surface thereof which faces the gap and whichare configured to distribute the fluid into the gap.
 18. The gear pumpof claim 17, wherein the plurality of distribution grooves extend froman outer circumference to an inner circumference of the thrust ringportion.
 19. The gear pump of claim 17, wherein the plurality ofdistribution grooves extend from an outer circumference of the thrustring portion to a predetermined distance from the inner circumference ofthe thrust ring portion.
 20. A gear pump comprising: a gear wheel; anannular gear; a thrust ring; a housing having a fluid delivery chamberand a cover portion configured for placement such that a gap is formedbetween the thrust ring and the cover portion; and a fluid connectingpassage through a fluid flows from the fluid delivery chamber to the gapto thereby form a hydrodynamic lubricating film in the gap which reducesoperational friction between the thrust ring and the cover portion,wherein: the fluid connecting passage has a first connecting groove incommunication with the fluid delivery chamber, a second connectinggroove in communication with the first connecting groove, and a thirdconnecting groove in communication with the second connecting groove andthe gap, and the thrust ring has a plurality of distribution grooves ona surface thereof which faces the gap and which are configured todistribute the fluid into the gap.